In the manufacture of translucent containers such as clear or colored glass bottles, it is important to maintain dimensional parameters of each container within design specifications for both functional and aesthetic reasons. For example, it is important that the finish of the container, including particularly the container mouth, possess desired geometric characteristics so that the container can be accepted by automatic filling and capping equipment without damage to the equipment, fracture of the container or jamming of the process line.
U.S. Pat. No. 3,313,409, assigned to the assignee hereof, discloses a container inspection system in which containers are routed in sequence through a plurality of inspection stations at which various geometric and other properties are measured. At one such station, an attempt is made to insert a plug of predetermined size into the mouth of the container. The diameter of the plug is coordinated with minimum container mouth diameter for mating with container filling equipment, for example. If the plug cannot be so inserted into the container mouth, the container is rejected. At other stations of the inspection system, container dimensional parameters are measured by monitoring the position of rollers in contact with the container as the container is rotated.
Although the system disclosed in the noted patent has enjoyed substantial commercial acceptance and success, improvements remain desirable. The inspection techniques that require physical contact with the container are slow, and are subject to mechanical wear of the rollers and plugs, for example. The reciprocating motions needed to bring the plugs and rollers into and out of contact with the container draw substantial amounts of electrical power. It is a general object of the present invention to provide an apparatus and method for inspection of container parameters, including particularly inside diameter of the container mouth, that have no moving parts (other than the container itself) or parts in contact with the container, that are more economical and efficient than inspection techniques heretofore proposed, and afford reliable service over an extended operating lifetime.